Hybrid welding is a process in which the techniques of energy beam welding and gas metal arc welding (GMAW) are combined. As a result, the high speed and large penetration depth associated with e.g. laser welding can be obtained at the same time as the excellent gap-bridging capabilities associated with GMAW. Hybrid welding is widely applied to join together steel parts. However, when one or both of the steel parts are made of a hardened steel with a high carbon content, i.e. greater than 0.4% C, welding is more problematic. The melting of the weld materials and overheating of the materials next to the weld (Heat Affected Zone (HAZ)) can result in unwanted phase transformations, leading to over-hardening and possibly cracking.
A weld joint formed in a hybrid welding process applicable to hardened metal parts is disclosed in DE 102006021911. The joint is formed by injecting energies from carbon dioxide laser welding and metal protective gas welding into a common process zone, and supplying a welding filler material into a welding bath melted by the welding process. The arc welding energy source foreruns the laser welding energy source by about 2-10 mm. The welding filler material, AWS standard ER NiCr-3, is supplied in form of wire with diameter of 0.8-1.2 mm and with a feed speed of 5-22 m/min. In one embodiment, at least one of the parts is made of a case-hardened steel with a carbon content of 0.5-1.0% and a hardening depth of 0.1 to 1.2 mm.
There is still room for improvement, however, in terms of providing a weld joint that is suitable for through-hardened bearing steel.